In electronics, a switch is an electrical component that can break an electrical circuit, for example, to interrupt the current flow or divert the current from one electrical path to another. One type of electrical switch is the circuit breaker, which is an automatically operated electrical switch designed to electrically engage and disengage a selected circuit from an electrical power supply, for example, to protect the circuit from damage that can be caused by an overload or a short circuit. In general, a circuit breaker detects a fault condition, such as an overcurrent condition, and responsively discontinues electrical flow (i.e., “trips the circuit”), which is typically achieved by opening operating contacts within the circuit breaker to interrupt the current flow. To resume normal operation, the circuit breaker can normally be reset, either manually or automatically. Circuit breakers are manufactured in various sizes and configurations, from small safety breakers that protect an individual household appliance up to large switchgear designs for protecting high voltage circuits which distribute electricity to an entire town.
In many electrical supply systems, there are applications where a circuit must switch between alternate sources of electric power. For instance, many commercial buildings, residential homes, and industrial facilities need the capacity to switch from a standard utility power source to a back-up power generator. A common application of this type of arrangement is known as a “transfer switch.” To support these applications, some circuit breaker boxes are designed with separate electrical circuits that are arranged so that when one group of circuits is switched to a conductive state, another group of circuits is switched to a non-conductive state in alternating fashion. In some arrangements, a common load can be alternately switched between separate power sources so that as one power source is disconnected from the load the second power source is connected after a negligible delay.
In many common circuit breaker box designs, the individual breaker switches are packaged such that switches that are connectable to related circuits are arranged in horizontally or vertically opposing in-line pairs. To accomplish a switching operation, such as those described above, one switch is flipped (opened or closed) before a second switch of a functional pair is flipped (closed or opened). In a transfer switch application where the breaker switches are manually operated, the operator will flip the transfer switches by hand, first disconnecting the utility current source from the circuit and then connecting the back-up generator to the circuit (and vice versa). Manually operated breaker switches are typically spring biased so that once a switch handle has reached top dead-center, any slight deflection from that position will cause the switch to continue to the fully switched position, unless otherwise restrained.
Separately acting switches are used in safety circuit breaker assemblies to ensure that the utility current circuitry is disengaged before a separate power source is connected, thereby preventing electricity from being fed back into the utility circuit. In addition, interlock mechanisms have been created that prevent one switch, which engages a first power source, from being closed at the same time a second switch in a functional pair, which engages another power source, is closed. Most interlock mechanisms are comprised of a slidably mounted blocking plate that can be moved rectilinearly between two operating positions. When in the first operating position, the blocking plate prevents a first switch handle from being closed while permitting a second switch handle to be closed. The blocking plate can then be slid to the second operating position, whereat the plate prevents the second switch handle from being closed while allowing the first switch handle to be closed.
Prior art switch interlock mechanisms for in-line opposed switches tend to be unnecessarily complex mechanisms, requiring a large number of components and moving parts to provide the blocking feature. The complexity of such devices increases manufacturing and assembly costs, and creates a higher likelihood of warranty claims for broken devices. In addition, a large amount of packaging space is consumed to accommodate the linear movement of the blocking plate, namely the multiple operating positions. Thus, there is a need for electrical switch interlock mechanisms that prevent multiple switches in a functional group from being engaged at the same time, while not requiring a large number of components or a lot of packaging space to properly operate.